I. Field of the Invention
This invention relates to indexable inserts for cutting tools, i.e. cutting inserts having plural cutting edges and suitable for mounting in plural orientations in cutting tools such that in each orientation one or more cutting edges are exposed for use. In particular, this invention relates to indexable inserts for turning operations.
II. Description of Related Art
Indexable inserts of interest herein have top and bottom surfaces of polygonal shape joined by side surfaces, intersections of at least portions of the side surfaces with the polygonal surfaces defining cutting edges of the insert. In general, turning operations are performed so that cutting occurs at an insert corner formed by intersections of sides at corners of a polygonal surface, the insert corner being traversed along a workpiece surface as the workpiece rotates. As is well known, turning operations performed in this way, cause the workpiece surface to be grooved as illustrated in FIG. 1. In applications where the surface roughness presented by such grooves is unacceptable, additional machining operations, such as grinding, must be performed to reduce or eliminate the surface roughness. The insert corners at which such cutting is performed are curved, rather than sharp, the corner radius providing resistance of the corner to chipping and breaking under load. It is also known that for a particular insert style and size applied at particular turning parameters, the larger the corner radius the smaller the depths of grooves in the workpiece surface. Nevertheless, some applications require that the corner radius be kept small, such as those requiring relatively sharp corners in workpiece surfaces. Hence, there remain conflicting demands for turning tools, i.e., the need to produce surfaces with little or no grooving and the need to maintain small corner radii to accurately produce workpiece features requiring relatively sharp corners.
In recent years, turning inserts have been made available to address conflicting demands of improved surface finish and relatively small corner radii for indexable turning inserts. In these inserts, corner radii are kept small and adjacent the corner radii there are provided side segments intended to increase the contact area of the insert with the workpiece to reduce the magnitude of grooves. Turning inserts are now known that provide curved segments adjacent the corner radius wherein the radii of the curved segments are larger than the corner radius. It is also now known to provide indexable turning inserts wherein flat segments are interposed between the corner radius and the sides, the flat segment blending smoothly with the curved corner and intersecting the side at a shallow angle. These segments, whether curved or flat, have become known as xe2x80x9cwipersxe2x80x9d, for their effect on reducing the magnitude of grooves produced by the insert as compared to performance of cutting inserts lacking such segments. While known wipers have achieved improved cutting performance, the desire for increased material removal rates from cutting tools has led to the need for further performance improvements.
It is an object of the present invention to provide indexable turning inserts having relatively small corner radii and plural segment wipers adjacent the corners
It is a further object of the present invention to provide an indexable turning insert having relatively small corner radii and wipers comprising a curved segment of relatively large radius adjacent the corner and a flat segment adjacent the curved segment and intersecting the insert side at a shallow angle.
Further objects and advantages of the invention shall be made apparent from the accompanying drawings and the following description thereof.
In accordance with the aforesaid objects the present invention provides an indexable turning insert having main upper and lower surfaces of polygonal shape joined by side surfaces. Insert corners are defined by the intersection of insert sides at each corner of the polygonal surfaces, insert corners having a curve of relatively small radius defining the nose of the corner. Adjacent the corner nose are wipers of plural segments, including at least one curved segment joining the corner radius and defined by a radius larger than the corner radius and at least one flat segment intersecting the insert side at a shallow angle.